Thomas Aquinas, Compendium of Theology

As Christ destroyed our death by His death, so He restored our life by His resurrection. Man has a twofold death and a twofold life. The first death is the death of the body, brought about by separation from the soul; the second death is brought about by separation from God. Christ, in whom the second death had no place, destroyed both of these deaths in us, that is, the bodily and the spiritual, by the first death He underwent, namely, that of the body.

Similarly, opposed to this twofold death, we are to understand that there is a twofold life. One is a life of the body, imparted by the soul, and this is called the life of nature. The other comes from God, and is called the life of justice or the life of grace. This life is given to us through faith, by which God dwells in us, according to Habacuc 2:4: "The just shall live in his faith."

Accordingly, resurrection is also twofold: one is a bodily resurrection, in which the soul is united to the body for the second time; the other is a spiritual resurrection, in which the soul is again united to God. This second resurrection had no place in Christ, because His soul was never separated from God by sin. By His bodily resurrection, therefore, Christ is the cause of both the bodily and the spiritual resurrection in us.

However, as Augustine says in his commentary on St. John, we are to understand that the Word of God raises up souls, but that the Word as incarnate raises up bodies. To give life to the soul belongs to God alone. Yet, since the flesh is the instrument of His divinity, and since an instrument operates in virtue of the principal cause, our double resurrection, bodily and spiritual, is referred to Christ's bodily resurrection as cause. For everything done in Christ's flesh was salutary for us by reason of the divinity united to that flesh. Hence the Apostle, indicating the resurrection of Christ as the cause of our spiritual resurrection, says, in Romans 4:25, that Christ "was delivered up for our sins and rose again for our justification." And in I Corinthians 15:12 he shows that Christ's resurrection is the cause of our bodily resurrection: "Now if Christ be preached, that He rose again from the dead, how do some among you say that there is no resurrection of the dead?"

Most aptly does the Apostle attribute remission of sins to Christ's death and our justification to His resurrection, thus tracing out conformity and likeness of effect to cause. As sin is discarded when it is remitted, so Christ by dying laid aside His passible life, in which the likeness of sin was discernible. But when a person is justified, he receives new life; in like manner Christ, by rising, obtained newness of glory. Therefore Christ's death is the cause of the remission of our sin: the efficient cause instrumentally, the exemplary cause sacramentally, and the meritorious cause. In like manner Christ's resurrection was the cause of our resurrection: the efficient cause instrumentally and the exemplary cause sacramentally. But it was not a meritorious cause, for Christ was no longer a wayfarer, and so was not in a position to merit; and also because the glory of the resurrection was the reward of His passion, as the Apostle declares in Philippians 2:9 ff.

Thus we see clearly that Christ can be called the first-born of those who rise from the dead. This is true not only in the order of time, inasmuch as Christ was the first to rise, as was said above, but also in the order of causality, because His resurrection is the cause of the resurrection of other men, and in the order of dignity, because He rose more gloriously than all others.

This belief in Christ's resurrection is expressed in the words of the Creed: "The third day He arose again from the dead."